<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
<script>
    //toUpperCase() toLowerCase() 将字符串转换成大写/小写
    var str = "HELLO JAVASCRIPT";
    var str1=str.toLowerCase();
    var str2=str1.toUpperCase();
    document.write(str1);
    document.write(str2);

    /**
     * 字符串方法总结
     * length indexOf 
     * charAt(i) str[i] 获取索引位置字符
     * slice(start,end)
     * split(separator)
     * +
     * for
     * toUpperCase() toLowerCase()
    */
</script>
</html>